For GNOME development releases, see the schedule at http://live.gnome.org/action/edit/TwoPointNinetyone/. These get smoke-tested by the release-team and get some community testing as well. A considerable amount of testing comes in the form of having GNOME development versions in rawhide (currently 2.91.5). There are several Fedora test events scheduled to test various aspects of GNOME 3 (see QA/Fedora_15_test_days)

Features

it was just an experiment that did not work out; it is not part of the final GNOME 3 design

How should multi-monitor support behave with GnomeShell in Fedora 15?

Currently, gnome-shell just treats any additional monitors as extra space to put windows in but otherwise more or less ignores them. When you go into overview mode, it only takes effect on one screen, the others are just left blank. There's nothing yet done to integrate the workspace model the Shell encourages with multi-monitor setups. There's a bug for this, but again, AFAICT no particular commitment to fixing it up before the 3.0 release. (This isn't actually much of a 'regression' compared to GNOME 2, which was similarly lax about doing much with extra screens, but it's the sort of thing people might expect GNOME 3 to have fixed).

There are some ways in which multi-monitor support is better in GNOME3 than in 2.x:

* On the secondary monitor, dragging the window to the top edge maximizes

* We have working configuration for primary monitors in the control-center display panel

We are also hoping to have working barriers in X soon, so that we can improve the situation when the 'hot corner' is at a shared edge. Barriers have been promised for F15.

Workarounds

What is the procedure to manually revert to fallback mode?

Fallback mode is just that: a fallback. Therefore it is not planned to have a manual 'choose your UI' UI. You can of course open the hood and rewire what gnome-session does in the files /usr/share/gnome-session/sessions/gnome.session and /usr/share/gnome-session/sessions/classic-gnome.session. Doing so might void your warranty...